This invention relates to a switcher for flexibly interconnecting communication ports.
A television post production facility comprises an ensemble of machines of various types, such as editors, digital video effects devices, and video tape recorders (VTRs). During an editing session, the producer employs an editor to control the operations (playback, record, etc.) performed by the other machines to produce a final master tape.
In a given post production facility, several editing sessions, each requiring use of an editor and two or more other machines, may be conducted at any given time, and during a given editing session the producer might wish to add and drop machines from and to the suite of machines that are being used in the session.
In order to allow an ensemble of machines to be interconnected in a flexible fashion in different suites, without needing to swap cables whenever a change is desired, the machines may be connected to a digital routing switcher. The communication port of each machine includes at least one driver and at least one receiver, and the switcher forms a forward bus and reverse bus to which the drivers and receivers are connected.
In general, one of the machines is designated a source machine and transmits command messages to the other machines over the forward bus. The other machines, designated destination machines, receive the message from the source machine and generate response messages. In order to prevent a collision of response messages, a single destination machine is designated as the responding machine and the response messages of the other destination machines are blocked. When a suite is changed by adding or dropping a machine, it is difficult and inconvenient to keep track of the most recent configuration of the added or dropped machine and make sure that the machines of the new suite are properly configured.
In the case of a post production facility, the editor is generally the source machine and the destination machines are VTRs. The editor typically can support several forward buses and several reverse buses, so that the suite of machines controlled by a single editor may be composed of several subsuites of machines.
As described in the co-pending application, a port that is connected to the reverse bus may degrade the characteristics of the bus. This problem arises particularly when the suite of machines being used in an edit session is changed, since unless a machine that is dropped is switched off, it remains on the bus and it may generate response messages.